Flow control (solutions)

Primary exercises

A function with if/else statements.

Let’s take the following from a World Health Organization document:

An adult is a person older than 19 years of age unless national law defines a person as being an adult at an earlier age.
An adolescent is a person aged 10 to 19 years inclusive.
A child is a person 19 years or younger unless national law defines a person to be an adult at an earlier age.
However, in these guidelines when a person falls into the 10 to 19 age category they are referred to as an adolescent (see adolescent definition).
An infant is a child younger than one year of age.

The categories can be enumerated as follows:

group	condition for age [y]
`adult`	`age > 19`
`adolescent`	`age >= 10 && age <= 19`
`child`	`age >= 1 && age < 10`
`infant`	`age < 1`

Implement a function ageGroup which takes age argument (in years) and returns the age group label.

Function template Here is a template of the ageGroup function:

ageGroup <- function( age ) { 
  # age: age given in years
  ...
}

and here are expected results:

ageGroup(0)   # "infant"
ageGroup(10)  # "adolescent"
ageGroup(9)   # "child"
ageGroup(20)  # "adult"
ageGroup(-1)  # should generate an error

To generate the error we request the program to ?stop with an error message.

# 1) Poor implementation
#
ageGroup <- function( age ) { 
  # age: age given in years
  result <- "child"
  if( age > 19 ) {
    result <- "adult"
  }
  if( age >= 10 & age <= 19 ) {
    result <- "adolescent"
  } 
  if( age < 1 ) {
    result <- "infant"
  } 
  if( age < 0 ) {
    stop( "Age can't be negative." )
  } 
  result
}

# 2) Improved implementation 
# 
# In the previous scenario: when `age` is 30 and the `result` is set to `adult` 
# it makes no sense to check whether `age` is in other ranges,  
# `if`/`else` construction allows for that.
#
ageGroup <- function( age ) { 
  # age: age given in years
  if( age > 19 ) {
    result <- "adult"
  } else if( age >= 10 ) {
    result <- "adolescent"
  } else if( age >= 1 ) {
    result <- "child"
  } else if( age >= 0 ) {
    result <- "infant"
  } else {
    stop( "Age can't be negative." )
  }
  result
}

ageGroup(0)   # "infant"
[1] "infant"
ageGroup(10)  # "adolescent"
[1] "adolescent"
ageGroup(9)   # "child"
[1] "child"
ageGroup(20)  # "adult"
[1] "adult"
ageGroup(-1)  # should generate an error
Error in ageGroup(-1): Age can't be negative.

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